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Measuring Ripple Current
: rippel current -- LION	Post Reply	Top of thread	Engineering Forum

Posted by: Kelly Bramble ® 01/31/2011, 09:37:34 Author Profile eMail author Edit

Well, I did a search on GG for "Measuring Ripple Current" and found tons of information. It appears that one can hook an oscilloscope on to the circuit and look at the right scale. Or, one can "measure the AC voltage on the DC output of your supply by putting your DMM on "AC VOLTS" and multiplying what you read by 2.83. It won't be perfect because the ripple waveform won't be a sine wave, but it'll be close." https://sci.tech-archive.net/Archive/sci.electronics.basics/2006-06/msg00403.html Modified by Kelly Bramble at Mon, Jan 31, 2011, 09:38:06

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: Measuring Ripple Current
: Measuring Ripple Current -- Kelly Bramble	Post Reply	Top of thread	Engineering Forum

Posted by: LION ® 02/01/2011, 01:51:43 Author Profile eMail author Edit

Thanks for your explanation. Is measurement by DMM wii give me right information to decide that my rectifier of UPS or Charger is OK?

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: Measuring Ripple Current
: Measuring Ripple Current -- Kelly Bramble	Post Reply	Top of thread	Engineering Forum

Posted by: Pinkerton ® 01/31/2011, 21:36:11 Author Profile eMail author Edit

The only real way is using an oscilloscope. The step by step is simple. Adjust the scales until you can see the ripple then read off from the graticule and calculate from the scales. Using a DMM will only work if there is a large difference in the amplitude of the ripple over the quiescent. Something in the order of around 40% and higher, otherwise the DMM will try to average and ignore the ripple as a DMM has a finite sample time/period. A "ripple" of 40% is not a ripple, it is a huge transient or instability in the supply. If it is that bad, you have more problems than discerning "ripple." Dave

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: : Measuring Ripple Current
: : Measuring Ripple Current -- Pinkerton	Post Reply	Top of thread	Engineering Forum

Posted by: LION ® 02/01/2011, 01:59:42 Author Profile eMail author Edit

I definitely need to buy oscilloscope, I think. You suggest no more than 40% but in description of Charger's rectifier is ripple in Amps should not exceed 10% of the battery capacity in Ah at C8 rate of discharge.

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: : : Measuring Ripple Current
: : : Measuring Ripple Current -- LION	Post Reply	Top of thread	Engineering Forum

Posted by: Pinkerton ® 02/01/2011, 09:42:56 Author Profile eMail author Edit

Nope, I am saying that a DMM will not effectively identify ripple unless it is around 40% of the signal. For example, in a 10vdc circuit with 3v ripple, the DMM would probably not detect the ripple when using the AC scale. At 10vdc and 5v ripple, the DMM could indicate some ripple that may be able to be quantified, but not very accurately. You are confusing different things. The charger max 10% ripple is the maximum amount of ripple the battery will handle and still get charged without damage. The lower the ripple the better on a charging circuit. You could NOT measure battery-damaging-ripple using a DMM. Only an oscilloscope can do that accurately enough. Given your sign-on name, if you are messing with Lithium batteries, proceed with extreme caution. Designing chargers for Lithium batteries is not for the novice as the charging parameters are critical at all times. Check this... https://www.youtube.com/watch?v=-DcpANRFrI4 Dave Modified by Pinkerton at Tue, Feb 01, 2011, 10:48:00

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: : : : Measuring Ripple Current -- Pinkerton	Post Reply	Top of thread	Engineering Forum

Posted by: LION ® 02/02/2011, 07:29:14 Author Profile eMail author Edit

Thanks a lot Dave I really appreciate you I understand your consern and defenetly need to buy oscilloscope, just which type is more portable and useful for batteries rippel measur.(portable for me will be the best). What type you could suggest?

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: : : : : Measuring Ripple Current
: : : : : Measuring Ripple Current -- LION	Post Reply	Top of thread	Engineering Forum

Posted by: Pinkerton ® 02/02/2011, 09:42:10 Author Profile eMail author Edit

I have a TEK TDS-210. TEK is not the cheapest stuff but it will last forever and remain very accurate. For your needs a cheaper one would be fine for now but what about inn ten years time. Here's the minimum I would look for. Dual channel WITH 10x probes. Often scopes are sold without probes and they will add some more bucks to the real price. 50MHz or greater. 20MHz would be more than fine for what you want at the moment, but go as high as the bank account can handle. At least one channel with Storage so you can trap a scan and look at it later. Output to a PC is good also. Battery powered is nice. Check this before buying cheap... https://www.youtube.com/watch?v=-uSku1G4M6w&NR=1 Notice how the TEK (black and white) is rock steady and the other one is drifting between 10MHz and 20MHz. Ya gets what ya pays for. Dave

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: : : : : : Measuring Ripple Current -- Pinkerton	Post Reply	Top of thread	Engineering Forum

Posted by: LION ® 02/03/2011, 05:45:22 Author Profile eMail author Edit

THANKS A LOT DAVE! This one is the best for me. Are you electrician or? Could I have you email?

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: : : : : : : Measuring Ripple Current -- LION	Post Reply	Top of thread	Engineering Forum

Posted by: Pinkerton ® 02/03/2011, 09:30:35 Author Profile eMail author Edit

I am a Mechanical Engineer but I have a pretty good grasp on electronics too. You can email via this board. Dave

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